Boolean Operators are AND & OR. Both of these operators have a specific function.
AND
makes your search more specific, thus narrowing the results
OR
searches for clusters of related terms, thus broadening the results
(women OR woman OR female OR feminine)
Example:
Research Topic: impact of climate change on food security
Food Security AND (Climate Change OR Global Warming OR Climatic Changes)
Searching this way means that you will retrieve results about
Food Security AND Climate Change
Food Security AND Global Warming
Food Security AND Climatic Changes